Conventionally, an image forming apparatus comprises an automatic document feeder (ADF) for reading a document during a copying or scanning. When conveyed and read by the ADF, the document arranged on the ADF passes along the document glass for the ADF. Then, the passed along document is read by a reading unit consisting of an exposure lamp, a mirror or an image sensor. With an image forming apparatus or a reading apparatus provided with an ADF, pieces of documents can be conveyed to a reading position and successively read piece by piece.
However, the image of the document sometimes undergoes blown out highlights if the document is conveyed and read by the ADF. Especially for thin lines or a part light (pale) in color, it will cause blown out highlight easily. Thus, the reproducibility of the image on a document generated by the reading processing using the ADF is sometimes reduced, depending on the content of the image.